Within the art of semiconductor memory devices, the portions of a memory being subjected to a high number of programming cycles and erase cycles will tend to age faster than other portions being subjected to fewer programming cycles and/or erase cycles. Non-uniform aging of a memory device may result in different programming levels and erase levels which should be generated and applied to older memory segments compared to younger memory segments, and data in the older memory segments which are approaching the end of their service lifetime might require a transfer to younger memory segments. This may result in an increase of operation overhead of the memory device.
Wear leveling may be used to provide a more uniform aging across memory segments of a memory device, whereby an approximately equal number of programming cycles and erase cycles are applied to each memory segment. As a memory segment's age is closely related to the number of programming cycles and erase cycles the memory segment experiences, applying a generally equal number of programming cycles and erase cycles uniformly across the memory device may result in a reduction of variation of the aging of different memory segments within the memory device.
While a conventional wear leveling may help in reducing memory segment-to-memory segment aging variation, a significant variation still remains. By way of example, variations in semiconductor fabrication processes and environment/operating conditions across memory segments may cause different memory segments to age at varying aging rates.
Furthermore, a memory segment's program/erase level may be defined by an intermittent condition, e.g., a power anomaly or other temporary condition, which may not persist. A program/erase operation attempted during this time may fail, and a less favorable program/erase level (e.g., a higher program/erase level than actually needed) may be used for subsequent program/erase operations. The less favorable program/erase level may result in an unnecessary reduction of the service lifetime of the respective memory segment.